1. Field of the Invention
The present invention relates to an ITS (Intelligent Transport System) realizing road-road communication, which is wireless communication between roadside devices, road-vehicle communication, which is wireless communication between a roadside device and an in-vehicle device, and vehicle-vehicle communication, which is wireless communication between in-vehicle devices.
2. Description of the Related Art
FIG. 1 is a diagram explaining an overview of an Intelligent Transport System (ITS).
An ITS is a system for realizing smoother and safer traffic by exchanging traffic information between an in-vehicle communicator provided in a vehicle and a roadside communicator such as traffic signals provided at a roadside. FIG. 1 illustrates a system configuration of an ITS. ASN-GW (Access Service Network) is connected to a CSN (Connectivity Service Network), an upper-layer device for communication control. A base station 5 and a roadside device 6, which is a key device of communications on the road, are connected to ASN-GW. Other roadside devices and in-vehicle devices are present on the road. These devices communicate with the roadside device 6 while in the communication cell of the roadside device 6. In-vehicle devices are moving at all times and communicate with different roadside devices 6 one after another.
For wireless communications methods to realize such a system, the use of the IEEE standard 802.16 series wireless communication system has been proposed. The 802.16e is a standard relating to a communication method between BS (Base Station) and MS (Mobile Station) in which communications between BS and BS are performed by wired communications. The communication method does not allow one MS to directly communicate with another MS. For that reason, it is difficult to realize road-road communications and vehicle-vehicle communications. The 802.16j standardizes an RS (Relay Station) having a BS function, an MS function and a relay function. However, the Relay Station includes essentially only the relay function, not the real BS function and MS function. Therefore, it is still difficult to realize road-road communications, road-vehicle communications, and vehicle-vehicle communications.
Patent Document 1 discloses a roadside communication apparatus that allows a reduction in system cost.
[Patent Document 1]
Japanese Patent Application Publication No. 2006-163621